TOR actually amplifies the asymmetry betweem the NSA and smaller actors: the NSA by owning the whole network can easily break it, but it prevents smaller players from getting the same access.
Of course, the FBI seem to routinely compromise TOR sites they don't like.
How does Raspberry Pi help here? If it routes traffic at IP level, it will be transparent at an application level. Firewall/IDS won't help against zero days either.
It is just one potential brick in your security wall.
1) Pi only supports about 6MB/s on its ethernet port, meaning that you get 3MB/up and 3MB/down
2) TOR itself is just super slow, so why am I paying for a 350Mbps connection?
3) Most VPN services are fast enough for the above bandwidth, and offer sufficient security against state-based snooping.
They also claim Silk Road was classical hacking, but given what we know of parallel construction and their vagueness in describing their locating of the servers, we can't really know what happened there.
edit: in the interests of clarification, this means I expect to see attacks on Tor within the US before the UK.